The present invention provides novel compounds having an effect of inhibiting (antagonizing) the action of a melanocyte-stimulating hormone (melanotropin; hereinafter referred to as MSH) which activates function of the melanocytes, melanin producing cells in vivo. The present invention also relates to an external preparation to be applied to the skin which is capable of preventing or relieving the symptoms of chloasmata or freckles caused by, for example, an excess production of melanin by enhanced melanocyte function.
MSH is a peptide hormone contained in various vertebrate animals, and .alpha.-, .beta.- and .gamma.-MSH have been known. It is known that they interact with a receptor on the melanocyte surface to successively activate adenylate cyclase and tyrosinase, and to accelerate melanine production. Among them, the effect of .alpha.-MSH is particularly strong.
Various processes for inhibiting the function of melanocytes were proposed heretofore. They include, for example, a process wherein an inhibitor which reacts on the tyrosinase in the melanocytes is used. Kojic acid is practically used as the inhibitor as described in Japanese Patent Unexamined Published Application (hereinafter referred to as as `J.P. KOKAI`) Nos. 53-3538, 53-6432 and 53-18739. However, the conventional processes are not necessarily satisfactory from the viewpoints of effect and safety. Further the use of a substance which inhibits the effect per se of the melanocyte-stimulating hormone has scarcely been reported heretofore.